There exist articles which are coated or impregnated with useful substances intended to be utilized when the article is contacted with a target surface. While there are advantages with having the substance present on or near the surface of such articles, there is often the drawback that the useful substance is unprotected and is subject to inadvertent contact before intended use. One broad category of such articles encompasses the area of tapes and labels.
In the art of tapes, labels, and other articles using pressure sensitive adhesive to adhere an adhesive coated surface to a target surface, there has been recognized the problem of premature sticking to the target surface. That is, before the adhesive coated surface can be properly positioned over a target surface, inadvertent contact of the adhesive with the target surface causes premature sticking at one or more locations, thereby inhibiting proper positioning. Premature sticking may also cause contamination or degradation of the adhesive prior to final positioning at the target surface.
Others have attempted to overcome this problem by providing standoffs on a material surface, between which adhesive elements are located. Standoffs include any means extending outwardly from an adhesive surface which is contacted first before the adhesive surface is exposed to contact by another surface. Protecting an adhesive from premature contact by another surface has been achieved by adding strips of polymer foam to form deformable standoffs on an adhesive surface, for example. Polymer foams, however, tend to spring back and exert a peel force on the adhesive bond to the target surface. Thus, a more aggressive adhesive may be required to overcome this undesirable peel force.
U.S. Pat. No. 5,141,790 to Calhoun et al. discloses one-time repositionable pressure sensitive tapes with an adhesive coated surface having clumps of particles spaced out on the adhesive to keep the adhesive from touching a target surface until the sheet is pressed against the target surface. The particles are smaller than the thickness of the adhesive layer so that when pressed, the particles sink below the surface of the adhesive and no longer provide their spacing function. Since adhesive may be the most expensive component of a tape, and since the overall surface is coated with a thick layer of adhesive, Calhoun et al. would offer an expensive solution.
U.S. Pat. No. 4,061,820 to Magid et al. discloses a foam with cells. The foam is compressed to open cell cavities at the foam surface so that pressure sensitive adhesive can be applied to the open cells. When the foam is released, the cells close and hide the adhesive. When the foam is pressed, the cells bring pressure sensitive adhesive to the surface for sticking the foam to a target surface. This too is believed to be an expensive solution to the problem, and defining continuous or interconnected patterns of adhesive would not be possible. Also, polymer foams provide undesirable spring back force, which acts to undo the adhesive bond to a target surface. Furthermore, in some applications transparency may be beneficial, such as for accurate placement, and the foam of Magid et al. would not be transparent.
U.S. Pat. No. 4,959,265 to Wood et al. discloses an adhesively coated substrate having bluntly pointed stems protruding beyond a layer of pressure sensitive adhesive. The back of this substrate may be bonded to a sanitary napkin. The napkin may then be installed onto a foraminous fabric by pressing to force the stems to penetrate the fabric to a depth where the fabric contacts the adhesive. By penetrating fabric, the stems significantly reinforce the adhesion of the fastener. The stems should be resistant to compression and bending, even thought they may be quite supple. The backing with its stems preferably is formed from a tough thermoplastic resin by cast molding or extrusion molding. The stems protrude 20 microns to 3 mm above the adhesive level, depending on the coarseness of the fabric to be penetrated. The adhesive area is preferably between 3 and 30 times the area occupied by the stems. Rigid target surfaces are obviously inoperable with Wood et al.
U.S. Pat. No. 5,344,693 to Sanders discloses a substrate having a plurality of non-interconnecting spacing means extending outwardly from an adhesive coated surface to space the surface from another surface until the surfaces are pressed together. The spacing means of Sanders is non-deformable. The spacing members are spaced up to 80 times the dimension of each spacer. Since few spacing members provide the standoff function, Sanders would need a stiff web between members as well as stiff members to prevent inadvertent adhesive contact. Stiffness in Sanders' configuration corresponds to thick, and therefore expensive materials. Sanders discusses his invention for use with reclosable bags. Sanders, like Wood et al., would not be compatible with rigid target surfaces where the members deform instead of the target surface.
A commonly assigned, co-pending U.S. patent application, Ser. No. 08/584,638, filed Jan. 10, 1996 by the same inventors as in the present application, discloses a film formed to have deformable hollow protrusions which are very closely spaced and a continuous layer of pressure sensitive adhesive located between the protrusions. This co-pending application is hereby incorporated herein by reference. The close spacing between protrusions enables the web material to be very thin and flexible yet resistant to inadvertent deformation because of the high density of standoffs per unit area. However, the co-pending application focuses on formed films which have pressure sensitive adhesive between protrusions. The same inventors have discovered much broader constructions for their new material, as well as alternative methods of making it.
Methods for making articles and surfaces having adhesive surfaces protected by standoffs are disclosed, for example, in U.S. Pat. No. 5,453,296 to Lauritzen et al. Lauritzen et al. describes methods for making a sanitary napkin which has a recessed adhesive pattern for attaching it to a user's undergarment. Lauritzen et al. forms depressions in a fluid-impervious barrier film. The depressions create raised areas in the barrier film on the side of the napkin which attaches to the undergarment. Adhesive is placed onto the barrier film side having the raised areas in discrete patterns between the raised areas. In an alternative, Lauritzen et al. applies adhesive to the tips of the raised areas of the barrier film and then inverts the raised areas to form depressions. The adhesive is thereby conveniently placed in the depressions. Lauritzen et al.'s discrete adhesive placement fails to enable an air-tight adhesive seal with a target surface, however.
Lauritzen et al. also notes that standoffs must be formed such that they are strong enough to protect the adhesive from inadvertent contact during shipping and storage, yet are deformable for activation. Lauritzen et al. states that sufficient rigidity is available from 0.03 inch (0.08 cm) to 0.06 inch (0.15 cm) thick foam. In one embodiment, conical depressions have diameters at their open ends of 0.1 inches (0.25 cm) to 0.5 inches (1.27 cm) and depths of 0.1 inches (0.25 cm) to 0.25 inches (0.64 cm). Such large depressions and thick foam preclude the ability to wind up the material in a compact roll for consumer delivery. Also, large sized standoffs provide greater opportunity for an interrupted seal instead of a continuous seal, especially when dealing with a narrow target surface. Smaller, more closely spaced standoffs increase the frequency of adhesive contact to the target surface to better approximates a continuous seal.
In still another Lauritzen et al. embodiment, a printing device transfers adhesive to a printing belt, which transfers adhesive to a release belt, and then to the barrier foam web. This system is used to first print a pattern of discrete patches of adhesive onto the barrier foam web. Then the foam web is registered with a vacuum plate. When each patch of adhesive is disposed above a recess in the forming plate, vacuum forms adhesive containing depressions. Because of registration requirements, the invention is believed limited to relatively large and well spaced standoffs. A fine pattern of very small standoffs would be difficult to make using Lauritzen et al.'s methods because registration for forming would require high accuracy. Lauritzen et al.'s methods are believed to limit material constructions to those having macro patterns of low number density of standoffs, compared to the micro pattern of high number density of standoffs of co-pending U.S. patent application, Ser. No. 08/584,638.